Flail tree processing units have been known for many years and initially were used for removing bark from logs. Typically one such device is disclosed in Canadian Pat. No. 454,353 issued Feb. 1, 1949 to D. Mathewson et al. In later developments the flail units were utilized to remove limbs from the trunk of a tree as exemplified by Horncastle Canadian Pat. No. 598,362 issued May 17, 1960. The Horncastle device consists of a pair of driven flail units spaced apart from one another and between which a single tree is propelled endwise by a conveyor. In a later development as exemplified by Canadian Pat. No. 964,965 issued Mar. 25, 1975 to S. Michael, a number of trees are delimbed simultaneously by moving a flail unit longitudinally along a pile of trees lying on the ground.
In using flail delimbers there are two dominant factors which affect its effectiveness. One is impact which depends on speed, weight and length of the chain utilized provided generally by design considerations and the other is control of the impact. This is necessary if one wishes to ensure the limb receives the maximum impact from the chain. In the prior art devices the control of impact has mainly been accomplished by the operator viewing the operation and manually adjusting the relative position of the flail unit and log or logs being processed. Since the operator's visibility of the flails acting on the trees is virtually nil, controlling the force of impact in this manner is no more than guesswork and is extremely inefficient. Thus, with the prior art devices many passes over a tree or group of trees, as the case may be, are required to provide a satisfactory limbing operation. With existing machines the number of passes required are four to six and even more in some instances.
Also, presently known flail delimbers consist of a single straight horizontal flail, as for example disclosed in the aforementioned Canadian Pat. No. 964,965, and it will be obvious that, when utilized on a pile of trees, not all of the flail units across the length of the flail drum contact the trees to be limbed with the same impact forces. This stems from the fact that when a pile of trees are lying on the ground there is a hump or crown to the pile and the link chains of the flail unit strike the trees on the higher part of the pile with greater force than those trees lying close to or on the ground at the edges of the pile. Thus, in a straight horizontal flail of the prior art devices, most of the energy is consumed at the high point of the pile (i.e. at the center of the pile) with less energy consumed on the outer edges. In this situation, if there is satisfactory limbing at the center of the pile, there will be unsatisfactory limbing, if any, at the outer edges of the pile.